I think that when it comes to going to a buffet, or any restaurant for that matter, that the key is to plan ahead-rather than sitting down while you are starving and ordering/putting on your plate whatever looks good at the time.
Even if it is a last minute trip that you were unprepared for-think about what to order while you are driving to the restaurant, or walking across the parking lot. If you use your "head" before you walk in, you gain some self control.
I often plan my meals this way. I don't avoid going to a restaurant-what I avoid is eating Pan Crust Meat Lover's pizza when my husband wants to go to Pizza Hut. If I inform myself beforehand and stay on top of what the restaurants are offering in some spare "surfing time" on the computer-than I am prepared when I go in. I have a couple slices of Thin N Crispy Veggie Lovers pizza with a Diet Pepsi or unsweetened tea-and I am completely satisfied for about 400-600 calories for dinner. (2 or 3 slices)
There are so many options that may not "sound" as good as something fattening, but they really are. Bob Evans has a wonderful vegetable beef soup that is lower calorie/lower fat-and it is wonderful and reminds me of my mother's. If the family wants to go there, then I order that, and the side order fresh fruit cup. I enjoy every minute of it because it is really good-even if it isn't pancakes or the pot pie.
At Panera Bread, I usually get a broth based soup, and the little cup of fresh fruit-and savor it.
At Starbucks, I get a skinny (nonfat) latte in the smallest size-it is basically black coffee and a serving of skim milk, so I get a skim dairy serving in. (You can get the nutritional info online or in their store pamphlet.) Add a dash of Splenda, and I am loving it...I don't need a 2,000 calorie humongo sized mocha with whipped cream.
I try not to think of it as "missing out" on anything. My tastes have actually changed in the past few years of eating healthy-so I would actually rather have whole wheat pasta or bread now instead of white...I would rather have sliced strawberries WITHOUT any sugary syrup in them...and I would rather have a soda or coffee with sweetener instead of a regular one. (They feel very syrupy on the tongue now.)
The main key for me, is to think about what I am going to get BEFORE I am asked by the waitress/register person. I can walk into the coffee shop expecting to order the nonfat latte-and do it-rather than going in, looking at the foo-foo drinks others are ordering, and saying to myself "Well that looks good-I might have one of those." It is just adjusting my thinking a little bit, I guess.